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Callback parameter needs an extra check

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
javascript
Domain
tooling

Research direction

Reproduce the supplied callback example with the static-eval entry point and inspect index.js around line 134, where the stack trace shows the property access failure. Trace how callback arguments are passed into the evaluator, then add a regression test covering the provided object input and verify that it completes without the reported TypeError.

Written by the indexing model from the issue text.

Description

My test code looks like this:

var evaluate = require('static-eval');
var parse = require('esprima').parse;

var src = 'foo(function (obj) { return obj.x })';
var ast = parse(src).body[0].expression;
var result = evaluate(ast, {
  foo: function (func) {
    return func({x: 1})
  },
});

console.log(result);

When I run it, I get:

$ node test.js
/home/stathis/src/jellyfish-jellyscript/node_modules/static-eval/index.js:134
                return obj[node.property.name];
                          ^

TypeError: Cannot read property 'x' of null
    at walk (/home/stathis/src/jellyfish-jellyscript/node_modules/static-eval/index.js:134:27)
    at walk (/home/stathis/src/jellyfish-jellyscript/node_modules/static-eval/index.js:152:20)
    at walk (/home/stathis/src/jellyfish-jellyscript/node_modules/static-eval/index.js:171:20)
    at walk (/home/stathis/src/jellyfish-jellyscript/node_modules/static-eval/index.js:112:25)
    at module.exports (/home/stathis/src/jellyfish-jellyscript/node_modules/static-eval/index.js:204:7)
    at Object.<anonymous> (/home/stathis/src/jellyfish-jellyscript/test.js:6:14)
    at Module._compile (internal/modules/cjs/loader.js:1068:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)
    at Module.load (internal/modules/cjs/loader.js:933:32)
    at Function.Module._load (internal/modules/cjs/loader.js:774:14)

whereas when I change

var src = 'foo(function (obj) { return obj.x })';`

to

var src = 'foo(function (obj) { return obj && obj.x })';`

I get a successful result:

$ node test.js
1

This looks like a bug to me, as my callback's input here is just {x: 1}, why would I need to make sure obj exists?

Dominant language
JavaScript
Stars
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Forks
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PR merge metrics
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